Add todo items for block references

TODO.md

@@ -28,3 +28,12 @@ the page, and the rows are the pages where these fields should be taken from.
 #### Show the values from the pages in a table form based on the header names
 
 #### Edit the values and update the name/value pair in the corresponding document
+
+## Block references
+
+- `((_[a-z0-9_]+))` block reference syntax
+- search blocks based on this syntax
+- load referenced blocks
+  - which blocks are referenced
+- `transform()` referenced blocks
+- /Block reference